Social scientists, economists, and philosophers have long been aware that some people are subject to a sort of half-time slump: a period when their well-being dips to an all-time low. What’s less clear is what causes this midlife ennui, which by many measures falls between a joyous childhood and contented retirement? Is it socioeconomic? Psychological? Metaphysical?

In this study, researchers first checked to see if the slump is uniquely human. They asked zookeepers to rate the relative happiness of some 500 chimps and orangutans, based on how often the apes seem to be in a good mood or how much pleasure they derive from socializing. Turns out our closest relatives also show a U-shaped curve of life satisfaction—cheery in youth and old age, and mopey in the middle.

So when you start lusting after that red convertible, you’re not totally bananas. You’re just going ape.